1. Field of the Invention
The invention concerns antenna systems for level measurement with a radar level measurement device.
2. Description of Related Art
Known from EP 1 058 341 A1 is a system made up of a wave guide for transmission of microwaves and an antenna at the front side end section of the wave guide. This system comprises a one-part component with an enlarged diameter at the front side end section that radiates the waves in the direction of the bulk material. While the wave guide with a smaller diameter is mono-modal, the front side section of the antenna with the larger diameter is capable of functioning in several modes. In the transmission area from the wave guide to the body of the antenna, a cross section adapter is employed in its cavity as a type of wave adapter. The cross section adapter is dimensioned in such a way that it does not permit the creation of any or only of an insignificant amount of higher modes than the base mode by the multi-modal antenna, and these are returned via the wave guide to a housing containing electronics for interpretation. The cross section adapter is constructed as a solid body from a dielectric solid body. In the direction of the front side, it projects tapered into the space of the antenna body. In the direction of the wave guide, the cross section adapter projects either tapered into the wave guide or as a blackbody with a flat transmission wall into the wave guide.
This arrangement makes it possible to transmit microwaves and/or radar waves from housing with suitable electronics, generally via a coaxial connector, a signal injection device, and the wave guide to the actual antenna. Horn, parabolic and rod antennas can be employed as antennas. In this arrangement, a section on the front side of the wave guide is at the same time constructed as a fastening element for fastening the overall system in a vessel wall. The fastening onto the wall of the vessel takes place in such a way that the antenna projects into the vessel in order to radiate microwaves and/or radar waves in the direction of a bulk material and to receive waves that are reflected by the surface of the bulk material in order to return them to the housing so that a level of the vessel can be determined.
Known from DE 197 03 346 A1 is a parabolic antenna for measuring the level in containers. For assembly and/or disassembly, the body of the parabolic antenna is constructed of individual antenna elements that can be pivoted towards the longitudinal axis of the arrangement, i.e., they can be folded up. As a result, when folded the parabolic antenna can be passed through a corresponding opening in the wall of the vessel. In this arrangement, a one-part antenna rod with a constant cross-section leads from a housing on the rear side that contains suitable electronics up to the end section on the front side on which a microwave transmitter and a microwave receiver are arranged. Waves that are fed via the antenna rod are transmitted from the microwave transmitter in the direction of the unfolded mirror body of the parabolic antenna in order to be radiated by the body of the antenna in the direction of the bulk material. Waves reflected by the bulk material are directed back to the microwave receiver by the body of the antenna and returned to the housing by the microwave receiver via the antenna rod.
In such an arrangement of a parabolic antenna with a flat body, large sections of which are aligned parallel to the surface of the bulk material, i.e. horizontal or nearly horizontal, the problem exists that dispersed bulk material remnants deposit on the antenna body.
Known from DE 197 03 346 A1 as a further feature is a cleaning device for cleaning the body of the parabolic antenna with compressed air or a cleaning fluid. Compressed air or a cleaning fluid is fed to jets, whereby the jets are directed toward the surface of the antenna and/or the mirror body via an inlet that runs parallel to the antenna rod as a self-contained component and is conducted through the overall system from the exterior area to the interior chamber of the vessel.
In many respects, this arrangement is complex in design because of the multitude of individual components and it also has a large exterior circumference.